1. Field of the Invention
The invention concerns an arrangement for radiation of a radio-frequency field into an examination subject in a magnetic resonance apparatus.
2. Description of the Prior Art
In magnetic resonance tomography, an examination subject is exposed to an optimally homogeneous, static basic magnetic field. This basic magnetic field is generated by a basic field magnet of the magnetic resonance apparatus.
Rapidly switched gradient fields for spatial coding of the magnetic resonance signals are superimposed on the basic magnetic field during the acquisition of the magnetic resonance images. The gradient fields are generated by gradient coils.
Radio-frequency pulses of a defined field strength are radiated into the examination subject with radio-frequency antennas. The magnetic flux density of these radio-frequency pulses is typically designated with B1; the pulse-shaped radio-frequency field is called the B1 field. Magnetic resonance signals that are acquired by radio-frequency acquisition antennas are triggered in the examination subject by the radio-frequency pulses.
Temporal and spatial fluctuations in the field strength of the exciting B1 field can lead to adulterated measurement results. These unwanted fluctuations in particular disruptively occur at magnetic flux densities of more than 1.5 Tesla.
To acquire magnetic resonance signals, radio-frequency acquisition antennas are used that are either permanently installed in the magnetic resonance apparatus or are fashioned to be movable, the latter being known as “local coil units”. These local coil units are specifically positioned close to the examination region and allow improved measurement results.
An arrangement in which the housing of a local coil unit for a magnetic resonance apparatus is fashioned such that at least one part of the housing embodies an insulating dielectric material is known from DE 103 45 176 A1. Inhomogeneities of the B1 field are thereby compensated in a passive manner in order to improve measurements on the examination subject.